Statistical Considerations in Meta-analysis

A meta-analysis of the accuracy of different measuring techniques to evaluate the marginal and internal gap of a fixed dental prosthesis: The American Academy of Fixed Prosthodontics, Research in Fixed Prosthodontics Committee

STATEMENT OF PROBLEM

Marginal gaps and the internal adaptation of a fixed dental prosthesis are important parameters related to a successful clinical outcome. Several methods have been used to measure these 2 parameters. In addition to conventional analog methods, digital methods have recently been developed. Nevertheless, statistical comparisons of these different approaches are scarce.

PURPOSE

The purpose of this study was to evaluate the results of the various measuring methods reported in the current literature and compare their results.

MATERIAL AND METHODS

An electronic literature search comprising articles published from January 1990 to June 2023was conducted through the MEDLINE (PubMed) and Web of Science databases. After a quality assessment screening, 17 articles were identified for inclusion in the meta-analysis. Data were used for the random-effects model, forest plots were drawn, and significance tests were conducted in the meta-analysis software program of the Cochrane Collaboration (RevManv5.3.5). Additionally, heterogeneity tests and a risk of bias analysis were performed.

RESULTS

In the general comparison of conventional and digital methods, the data did not show significant differences, and the results presented low homogeneity. When the cross-sectional method (CSM) was compared under a scanning electron microscope with the silicone replica Geomagic software program (SRG) method, CSM recorded significantly smaller gap values than SRG and presented high homogeneity. Meanwhile, in the comparison of CSM with the silicone replica technique (SRT) and the triple scan method (TSM), CSM recorded larger gap values than SRT and TSM, and the data did not show a significant difference. All of these results presented low homogeneity.

CONCLUSIONS

A comparison of most techniques revealed no significant differences in the internal and marginal gaps, except for SRG, which recorded significantly smaller gaps than CSM. However, the conclusions of these findings are limited because of concerns about bias and heterogeneity and because the found marginal gap data are just one way to assess the consistency and reliability of each method.

The synthesis of scientific shreds of evidence: a critical appraisal on systematic review and meta-analysis methodology

Synthesising results across studies to recognise the causes of variation in outcomes and to reach an overall understanding of a problem is a crucial part of the scientific method. Until in recent times, the results of scientific findings have been summarised in narrative reviews where the summary of transparent and objective results have become increasingly difficult. Systematic reviews and meta-analyses, conducted by subsequent strict protocols to guarantee reproducibility and decrease bias, have become more common in the synthesis of evidence.

Efficacy and safety of high-dose tigecycline for the treatment of infectious diseases: A meta-analysis

BACKGROUND

High-dose (HD) tigecycline regimen is increasingly used in infectious diseases, however its efficacy and safety versus low-dose (LD) is still unclear.

METHODS

A systematic review and meta-analysis was performed; PubMed, Embase, Cochrane Library, ScienceDirect, Web of Science, clinicalTrials.gov, Wanfang, VIP, and China National Knowledge Infrastructure (CNKI), were searched using terms "tigecycline" AND "dose" up to October 31, 2018. Eligible studies were randomized trials or cohort studies comparing mortality, clinical response, microbiological eradication and safety of different tigecycline dose regimens for any bacterial infection. The primary outcome was mortality, and the secondary outcomes were clinical response rate, microbiological eradiation rate and adverse events (AEs). Meta-analysis was done with random-effects model, with risk ratios (RR) and 95% confidence intervals (CI) calculated for all outcomes.

RESULTS

Of 951 publications retrieved, 17 studies (n = 1041) were pooled in our meta-analysis. The primary outcome was available in 11 studies, and the RR for mortality was 0.67 (95% CI 0.53-0.84, P < .001). Clinical response (RR 1.46, 95% CI 1.30-1.65, P < .001) and microbiological eradication rate (RR 1.61, 95% CI 1.35-1.93, P < .001) were both higher in HD than in LD tigecycline regimen. However, non-Chinese study subgroup presented no statistical significance between HD and LD regimen, RR for mortality, clinical response and microbiological eradication were 0.79 (95% CI 0.56-1.14, P = .21), 1.35 (95% CI 0.96-1.92, P = .26), 1.00 (95% CI 0.22-4.43, P = 1.00), respectively. AEs did not differ between HD and LD tigecycline (RR 1.00, 95% CI 0.80-1.26, P = .97).

CONCLUSION

HD tigecycline regimen reduced mortality meanwhile improved clinical efficacy and should be considered in serious infections caused by multidrug-resistant and extensively drug-resistant (MDR/XDR) bacteria.

Evaluation of maxillary anterior teeth width: A systematic review

STATEMENT OF PROBLEM

Estimating the width of the maxillary anterior teeth when creating an esthetic smile can be challenging. Valid metrics to assist in this process are needed.

PURPOSE

The purpose of this systematic review was to evaluate the validity of interalar distance and inner canthal distance with the golden proportion, golden mean, and recurring esthetic dental proportion in predicting intercanine distance and the combined width of central incisors to potentially provide a guide for tooth restoration.

MATERIAL AND METHODS

A literature search was conducted using PubMed, Medline, Google Scholar, EMBASE, CNKI, Web of Science, and the Cochrane Collaboration, identifying English- and non-English-language articles reporting on interalar width, inner canthal width, and maxillary anterior tooth width. Additional studies were identified by searching reference lists of the articles identified. Only studies that fulfilled inclusion criteria were included. Two examiners independently performed the literature search and data extraction. Using a meta-analysis software program, data extracted from each selected study were statistically combined using the random-effects model. Weighted mean differences, 95% confidence intervals, and heterogeneity were calculated for each measurement.

RESULTS

The search strategy resulted in a total of 282 articles, but only 41 articles fulfilling the inclusion criteria were included in the meta-analysis. The interalar distance was found to be significantly larger than intercanine distance, and the inner canthal distance was found to be substantially smaller than the intercanine distance. When predicting the central incisors combined width by interalar distance, both the golden proportion and golden mean predicted value were larger than the combined width of the central incisors. Only the recurring esthetic dental proportion (70%) predicted value showed no significant difference from the combined width of central incisors. When predicting the central incisors combined width by inner canthal distance, the golden proportion predicted value was larger than the combined width of central incisors, whereas both the golden mean and recurring esthetic dental proportion (70%) predicted value were found to be significantly smaller than the combined width of central incisors.

CONCLUSIONS

By analyzing the data from the literature, only the recurring esthetic dental proportion (70%) with interalar distance could be an accurate method for predicting the combined width of central incisors. Neither interalar distance nor inner canthal distance could directly be used to predict the intercanine distance.

An overview of the effect of sodium glucose cotransporter 2 inhibitor monotherapy on glycemic and other clinical laboratory parameters in type 2 diabetes patients

Objectives

We aimed to determine the effect of sodium glucose cotransporter 2 (SGLT2) inhibitor monotherapy on glycemic and other clinical laboratory parameters versus other antidiabetic medications or placebo therapy in patients with type 2 diabetes mellitus. In addition, we aimed to investigate the risk of diabetic ketoacidosis associated with SGLT2 inhibitor therapy and evaluate its weight-sparing ability.

Design

Meta-analysis.

Materials and methods

PubMed and MEDLINE were searched to identify eligible studies up to December 2015. Randomized controlled trials that assessed the efficacy and safety of SGLT2 inhibitor monotherapy versus placebo therapy or active control were considered. The Cochrane Collaboration Risk of Bias Tool was used to evaluate quality and bias. The mean difference was used to evaluate the glycemic and other clinical laboratory parameters for SGLT2 inhibitor intervention versus control by drugs or placebo. Similarly, the risk ratio was used to assess adverse events, and the I² was used to evaluate heterogeneity.

Results

SGLT2 inhibitors significantly decreased glycated hemoglobin (HbA1c) (P<0.001), weight (P<0.001), and the low-density lipoprotein/high-density lipoprotein ratio (P=0.03) compared with placebo therapy. No statistically significant changes were found in fasting plasma glucose, 2-hour postprandial glucose, or lipid parameters. Significant changes in the uric acid level were found for SGLT2 inhibitors versus placebo therapy (P=0.005) or active control (P<0.001). Although no significant change in levels of ketones occurred (P=0.93), patients receiving SGLT2 inhibitors were at greater risk of increased ketone bodies. Events suggestive of urinary tract infection and pollakiuria presented the greatest risk for patients receiving SGLT2 inhibitors versus active control or placebo therapy.

Conclusion

SGLT2 inhibitors significantly decreased HbA1c, body weight, and the low-density lipoprotein/high-density lipoprotein ratio and were found to be safe and well tolerated in type 2 diabetes mellitus patients. Further randomized control trials are required to establish their risk for ketoacidosis.

Supporting systematic reviews using LDA-based document representations

BACKGROUND

Identifying relevant studies for inclusion in a systematic review (i.e. screening) is a complex, laborious and expensive task. Recently, a number of studies has shown that the use of machine learning and text mining methods to automatically identify relevant studies has the potential to drastically decrease the workload involved in the screening phase. The vast majority of these machine learning methods exploit the same underlying principle, i.e. a study is modelled as a bag-of-words (BOW).

METHODS

We explore the use of topic modelling methods to derive a more informative representation of studies. We apply Latent Dirichlet allocation (LDA), an unsupervised topic modelling approach, to automatically identify topics in a collection of studies. We then represent each study as a distribution of LDA topics. Additionally, we enrich topics derived using LDA with multi-word terms identified by using an automatic term recognition (ATR) tool. For evaluation purposes, we carry out automatic identification of relevant studies using support vector machine (SVM)-based classifiers that employ both our novel topic-based representation and the BOW representation.

RESULTS

Our results show that the SVM classifier is able to identify a greater number of relevant studies when using the LDA representation than the BOW representation. These observations hold for two systematic reviews of the clinical domain and three reviews of the social science domain.

CONCLUSIONS

A topic-based feature representation of documents outperforms the BOW representation when applied to the task of automatic citation screening. The proposed term-enriched topics are more informative and less ambiguous to systematic reviewers.

Use and applications of systematic reviews in public health nutrition

Decisions related to a spectrum of nutrition-related public health and clinical concerns must consider many factors and are best informed by evaluating the totality and quality of the evidence. Systematic review (SR) is a structured process to evaluate, compare, and synthesize relevant evidence for the SR-specific question(s). Applications of SR are exemplified here through the discussion of four case studies: research agendas, nutrient reference intakes, dietary guidance, and practice guidelines. Concerns that SR cannot be effectively applied to nutrition evidence because of the lack of an unexposed comparator and the complex homeostasis in nutrition are discussed. Central to understanding the applicability of SR is its flexibility in defining key inclusion criteria and rigorous elements as appropriate for the SR-specific question(s). Through the reduction of bias and random error by explicit, reproducible, comprehensive, and rigorous examination of all of the evidence, SR informs the scientific judgment needed for sound evidence-based public health nutrition.

Estimating the size of key populations: current status and future possibilities

PURPOSE OF REVIEW

Estimation of key population sizes is essential for advocacy, program planning, and monitoring of HIV epidemics in these populations. A review of recent publications on population size estimation among key populations including MSM, people who inject drugs, and male and female sex workers was conducted to identify and assess current practices at the global level.

RECENT FINDINGS

Studies have used multiple methods including capture-recapture, service multiplier, and unique object multiplier. Other studies apply census and enumeration, often before implementation of a behavioral survey. Network scale-up is used infrequently. Newer methods or variations of existing size estimation methods have emerged that are applied solely within surveys.

SUMMARY

A range of size estimation methods is available. All methods rely on theoretical assumptions that are difficult to meet in practice, are logistically difficult to conduct, or have yet to be fully validated. Accurate and valid key population size estimates remain as necessary as they are challenging to undertake; the concurrent use of multiple methods may be justified to facilitate the triangulation and interpretation of the resulting estimates. Formative assessment can help inform the appropriateness and feasibility of different size estimation methods.

CD49d is the strongest flow cytometry-based predictor of overall survival in chronic lymphocytic leukemia

PURPOSE

Although CD49d is an unfavorable prognostic marker in chronic lymphocytic leukemia (CLL), definitive validation evidence is lacking. A worldwide multicenter analysis was performed using published and unpublished CLL series to evaluate the impact of CD49d as an overall (OS) and treatment-free survival (TFS) predictor.

PATIENTS AND METHODS

A training/validation strategy was chosen to find the optimal CD49d cutoff. The hazard ratio (HR) for death and treatment imposed by CD49d was estimated by pooled analysis of 2,972 CLLs; Cox analysis stratified by center and stage was used to adjust for confounding variables. The importance of CD49d over other flow cytometry-based prognosticators (eg, CD38, ZAP-70) was ranked by recursive partitioning.

RESULTS

Patients with ≥ 30% of neoplastic cells expressing CD49d were considered CD49d+. Decrease in OS at 5 and 10 years among CD49d+ patients was 7% and 23% (decrease in TFS, 26% and 25%, respectively). Pooled HR of CD49d for OS was 2.5 (2.3 for TFS) in univariate analysis. This HR remained significant and of similar magnitude (HR, 2.0) in a Cox model adjusted for clinical and biologic prognosticators. Hierarchic trees including all patients or restricted to those with early-stage disease or those age ≤ 65 years always selected CD49d as the most important flow cytometry-based biomarker, with negligible additional prognostic information added by CD38 or ZAP-70. Consistently, by bivariate analysis, CD49d reliably identified patient subsets with poorer outcome independent of CD38 and ZAP-70.

CONCLUSION

In this analysis of approximately 3,000 patients, CD49d emerged as the strongest flow cytometry-based predictor of OS and TFS in CLL.

Primary prevention of dental erosion by calcium and fluoride: a systematic review

BACKGROUND

Overviews of the current literature only provide summaries of existing relevant preventive strategies for dental erosion.

OBJECTIVES

To perform a systematic review according to the quantitative meta-analysis method of the scientific literature on prevention of dental erosion. The focused question will address primary prevention of dental erosion by calcium and fluoride.

MATERIALS AND METHODS

Randomized clinical trials (RCTs) regarding dental erosion prevention. The search included five databases: Embase, Cochrane database of systematic reviews, PubMed (MEDLINE), FDA publication and Berman medical library of the Hebrew University. The search included data in the English language, with effect on preventing dental erosion always presented as mean enamel loss and measured by profilometer. Statistical meta-analysis was performed by StatsDirect program and PEPI statistical software. Fixed- and random-effect models were used to analyse the data. Heterogeneity tests were employed to validate the fixed-effect model assumption.

RESULTS

A total of 475 articles on dental erosion prevention were located. A four-stage selection process was employed, and 10 RCT articles were found to be suitable for meta-analysis.

CONCLUSIONS

The number of studies on prevention of dental erosion maintaining standards of evidence-based dentistry remains insufficient to reach any definite conclusions. The focused questions of this review cannot be addressed according to the existing literature.

Efficacy and safety of intensified antiplatelet therapy on the basis of platelet reactivity testing in patients after percutaneous coronary intervention: systematic review and meta-analysis

BACKGROUND

ADP-specific platelet function assays were shown to predict thrombotic events, and might be helpful to select candidates for more potent antiplatelet therapy. We aimed to determine the efficacy and safety of giving intensified antiplatelet therapy on the basis of platelet reactivity testing for patients undergoing percutaneous coronary intervention (PCI).

METHODS

Electronic databases were searched to find prospective, randomized trials that reported the clinical impact of using an intensified antiplatelet protocol (repeated loading or elevated maintenance doses of clopidogrel, prasugrel or glycoprotein IIb/IIIa inhibitor) on the basis of ADP-specific platelet reactivity testing (VerifyNow, Multiplate, VASP or light transmission aggregometry) compared to standard-dose clopidogrel. Evaluated efficacy measures included cardiovascular death, non-fatal myocardial infarction and definite/probable stent thrombosis (ST), while major bleeding events were recorded as safety endpoint.

RESULTS

Between 2008 and 2011, 10 clinical trials comprising 4213 randomized patients were identified. Compared to standard antiplatelet therapy, the intensified protocol was associated with a significant reduction in cardiovascular mortality, ST and myocardial infarction (p<0.01 for all). There was no difference in the rate of major bleeding events between intensified and standard groups (p=0.44). Although the observed effects regarding mortality, ST and bleeding were not heterogeneous, meta-regression analysis revealed that the net clinical benefit of the intensified treatment significantly depended on the risk of ST with standard-dose clopidogrel (p=0.023).

CONCLUSION

Intensifying antiplatelet therapy on the basis of platelet reactivity testing reduces cardiovascular mortality and ST after PCI; however, the net benefit of this approach depends on the risk of ST with standard-dose clopidogrel.

Meta-analysis of food safety training on hand hygiene knowledge and attitudes among food handlers

Research has shown that traditional food safety training programs and strategies to promote hand hygiene increases knowledge of the subject. However, very few studies have been conducted to evaluate the impact of food safety training on food handlers' attitudes about good hand hygiene practices. The objective of this meta-analytical study was to assess the extent to which food safety training or intervention strategies increased knowledge of and attitudes about hand hygiene. A systematic review of food safety training articles was conducted. Additional studies were identified from abstracts from food safety conferences and food science education conferences. Search terms included combinations of "food safety," "food hygiene," "training," "education," "hand washing," "hand hygiene," "knowledge," "attitudes," "practices," "behavior," and "food handlers." Only before- and after-training approaches and cohort studies with training (intervention group) and without training (control group) in hand hygiene knowledge and including attitudes in food handlers were evaluated. All pooled analyses were based on a random effects model. Meta-analysis values for nine food safety training and intervention studies on hand hygiene knowledge among food handlers were significantly higher than those of the control (without training), with an effect size (Hedges' g) of 1.284 (95% confidence interval [CI] ∼ 0.830 to 1.738). Meta-analysis of five food safety training and intervention studies in which hand hygiene attitudes and self-reported practices were monitored produced a summary effect size of 0.683 (95% CI ∼ 0.523 to 0.843). Food safety training increased knowledge and improved attitudes about hand hygiene practices. Refresher training and long-term reinforcement of good food handling behaviors may also be beneficial for sustaining good hand washing practices.

Efficacy and safety of tigecycline for the treatment of infectious diseases: a meta-analysis

BACKGROUND

Multidrug resistance among bacteria increases the need for new antimicrobial drugs with high potency and stability. Tigecycline is one candidate drug, and a previous meta-analysis of only published randomised controlled trials suggested that it might as effective as comparator treatments; we did a meta-analysis to include new and unpublished trials to assess its efficacy for the treatment of adult patients with serious bacterial infection.

METHODS

We searched PubMed, Cochrane Central Register, and Embase up to March 30, 2011, to identify published studies, and we searched clinical trial registries to identify completed unpublished studies, the results of which were obtained through the manufacturer. Eligible studies were randomised trials assessing the clinical efficacy, safety, and eradication efficiency of tigecycline versus other antimicrobial agents for any bacterial infection. The primary outcome was treatment success in patients who received at least one dose of the study drug, had clinical evidence of disease, and had complete follow-up (the clinically assessable population). Meta-analysis was done with random-effects models because of heterogeneity across the trials.

FINDINGS

14 randomised trials, comprising about 7400 patients, were included. Treatment success was lower with tigecycline than with control antibiotic agents, but the difference was not significant (odds ratio 0·87, 95% CI 0·74-1·02). Adverse events were more frequent in the tigecycline group than in the control groups (1·45, 1·11-1·88), with significantly more vomiting and nausea. All-cause mortality was higher in the tigecycline group than in the comparator groups, but the difference was not significant (1·28, 0·97-1·69). Eradication efficiency did not differ between tigecycline and control regimens, but the sample size for these comparisons was small.

INTERPRETATION

Tigecycline is not better than standard antimicrobial agents for the treatment of serious infections. Our findings show that assessment with unpublished studies is needed to make appropriate decisions about new agents.

FUNDING

None.

Semi-automated screening of biomedical citations for systematic reviews

Background

Systematic reviews address a specific clinical question by unbiasedly assessing and analyzing the pertinent literature. Citation screening is a time-consuming and critical step in systematic reviews. Typically, reviewers must evaluate thousands of citations to identify articles eligible for a given review. We explore the application of machine learning techniques to semi-automate citation screening, thereby reducing the reviewers' workload.

Results

We present a novel online classification strategy for citation screening to automatically discriminate "relevant" from "irrelevant" citations. We use an ensemble of Support Vector Machines (SVMs) built over different feature-spaces (e.g., abstract and title text), and trained interactively by the reviewer(s).

Semi-automating the citation screening process is difficult because any such strategy must identify all citations eligible for the systematic review. This requirement is made harder still due to class imbalance; there are far fewer "relevant" than "irrelevant" citations for any given systematic review. To address these challenges we employ a custom active-learning strategy developed specifically for imbalanced datasets. Further, we introduce a novel undersampling technique. We provide experimental results over three real-world systematic review datasets, and demonstrate that our algorithm is able to reduce the number of citations that must be screened manually by nearly half in two of these, and by around 40% in the third, without excluding any of the citations eligible for the systematic review.

Conclusions

We have developed a semi-automated citation screening algorithm for systematic reviews that has the potential to substantially reduce the number of citations reviewers have to manually screen, without compromising the quality and comprehensiveness of the review.